1. Field of the Invention
The present invention relates to audio conferencing, and, in particular, to computer-implemented processes and computer systems for processing audio signals for open audio systems.
2. Description of the Related Art
A traditional telephone handset places the transmitter close to the user's lips and couples the receiver tightly to the user's ear. A speakerphone or other so-called open audio systems replace the handset with a separate microphone and loudspeaker that can be set on a table a few feet from the user. One problem with speakerphones results from acoustic coupling, where the sounds produced by the loudspeaker are picked up by the local microphone and retransmitted back to the sender. The result can be an undesirable echoing in which a talker hears his own voice delayed by the transmission to and retransmission from a remote speakerphone.
One known solution to the problems of acoustic coupling and echoing is voice switching, in which only one direction of transmission is fully active at a time. Systems for achieving this one-way-at-a-time (i.e., half duplex) communication determine which direction is to be active at a given time.
Referring now to FIG. 1, there is shown a circuit block diagram of a conventional speakerphone 10. FIG. 1 is based on FIG. I from the seminal article "Fundamental Considerations in the Design of a Voice-Switched Speakerphone" by A. Busala (The Bell System Technical Journal, Vol. XXXIX, No. 2, pp. 265-294, Mar. 1960). As shown in FIG. 1, the voltage levels of local audio signals generated by microphone 12 are attenuated by transmit attenuator 14 for transmission to a remote node. Similar, the voltage levels of remote audio signals received from the remote node are attenuated by receive attenuator 18 for play at loudspeaker 16. The amount of attenuation applied by attenuators 14 and 18 is dynamically controlled by control circuit 19.
To achieve the one-way talk state in which the user of speakerphone 10 talks to the remote participant, control circuit 19 causes receive attenuator 18 to attenuate significantly the remote audio signals received from the remote node, while transmit attenuator 14 permits transmission of the local audio signals to the remote node without significant attenuation. Similarly, to achieve the one-way listen state in which the user of speakerphone 10 listens to the remote participant, control circuit 19 causes transmit attenuator 14 to attenuate significantly the local audio signals, while receive attenuator 18 permits playback of the remote audio signals without significant attenuation.
In conventional systems such as speakerphone 10, the levels of attenuation are determined based on the volumes of the participants, as indicated by the voltage (or energy) levels of the remote and local audio signals. Thus, when one conversation participant starts to speak louder than the other, control circuit 19 controls the attenuation levels of the transmit and receive attenuators 14 and 18 to switch from the talk state to the listen state, or vice versa.
One of the problems with conventional speakerphone systems relates to cutoff, where the system incorrectly or prematurely changes the direction of communication, thereby cutting a talker off before he has completed. It is desirable therefore to provide voice-switched speakerphones that avoid or at least reduce undesirable cutoffs.
It is accordingly an object of the present invention to address the problems associated with undesirable cutoffs when using speakerphones or other open audio systems that rely on voice switching to avoid acoustic coupling.
It is a particular object of the present invention to provide open audio processing for computer-based audio/video conferencing systems.
Further objects and advantages of this invention will become apparent from the detailed description of a preferred embodiment which follows.